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ABSTRACT

The objective of this research effort was to evaluate the use of the Midwest Guardrail System (MGS) with reduced post embedment and potentially with reduced post spacing to satisfy Manual for Assessing Safety Hardware (MASH) Test Level 2 (TL-2) and TL-3 criteria when installed over low-fill culverts. The goal was to identify the shallowest post configuration that would meet TL-2 and TL-3 criteria, focusing on MGS post embedment depths between 28 and 40 in.

A series of bogie tests, test nos. LFCB-1 through LFCB-6, were performed on a steel W6x8.5 post embedded in MASH strong soil at 36, 32, and 28-in. embedment depths. These tests did not provide the desired data regarding the soil response due to yielding of the posts and relatively stiff soil. As such, three additional bogie tests, test nos. LFCB-7 through LFCB-9, were conducted on W6x16 steel posts with 40, 34, and 28-in. embedment depths. A W6x16 steel post was used to eliminate the possibility of post yielding for soil calibration purposes only. Next, the test results were used to develop simplified numerical modeling of the soil-post system under impact. The updated soil spring models were used in LS-DYNA models to replicate W6x8.5-post bogie tests (i.e., test nos. LFCB-1 through LFCB-6). Modifications were incorporated into the LS-DYNA models for a better prediction of overall post behavior. The validated soil spring models were incorporated into the full MGS model. A series of LS-DYNA simulations were conducted on the MGS with the shallowest embedment of 28 in. and standard embedment of 40 in. at TL-2 and TL-3 impact conditions, with full-, half-, and quarter-post spacings. Also, considering the variability of soil strength and its effect on soil-post behavior, a lower bound and an upper bound were adopted for the soil strength curve. In all simulations, the 2270P vehicle model was captured safely and all MASH criteria were met. Based on the simulation results, it was found that the MGS with the shallow embedment depth of 28 in. and half-post spacing would have dynamic deflection and working width similar to the baseline MGS with a 40-in. embedment depth and full post spacing at TL-2 and TL-3 impact conditions with no transition required. Thus, this MGS configuration was recommended for further full-scale crash testing under MASH test designation no. 3-11. 

KEYWORDS

Highway Safety, Crash Test, Roadside Appurtenances, Compliance Test, MASH 2016, Component Test, Reduced Post Embedment, MGS, Reduced Post Spacing, LS-DYNA

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